1. Field of the Invention
The present invention relates to an improved emulsion polymerization process utilizing ethylenically unsaturated amine salts of sulfonic, phosphoric and carboxylic acids. More specifically, the invention relates to emulsion polymerization processes which utilize ethylenically unsaturated amine salts of alkylbenzene sulfonic acids, alkyl olefin sulfonic acids, alkyl alcohol sulfuric acid esters, or alkoxylated alkyl alcohol sulfuric acid esters, fatty acids, and fatty phosphate acid esters, or mixtures thereof, to form polymers, discrete solid polymeric particles and latexes. Additionally, the present invention relates to the use of the salts to impart improved adhesion, hydrophobicity, resistance to film yellowing, scrubability, anti-blooming, hydrolytic stability and shear stability characteristics to polymer emulsions and latex formulations.
2. Description of the Related Art
The emulsion polymerization of ethylenically unsaturated monomers to form discrete solid polymeric particles for use in coating, sealant, adhesive and/or elastomer (CASE) applications is well known to the art. Conventional emulsion polymerization of ethylenically unsaturated monomers employs one or more water soluble surfactants to emulsify the monomers and the resulting polymer products, i.e., latexes. The monomers used in emulsion polymerization reactions are generally water-insoluble, but in some cases may be water-soluble. During a typical emulsion polymerization, a surfactant is used to suspend small portions of monomer in a continuous or semi-continuous aqueous phase. Typically, the monomer molecules are suspended as small spheres in the aqueous phase, wherein the polymerization takes place within the small spheres. The water soluble surface active agents, i.e., surfactants, typically utilized in emulsion polymerization reactions are anionic, nonionic, and cationic surfactants or a mixture thereof.
The polymeric particles formed by the emulsion polymerization process are typically utilized in coating, sealant, adhesive and/or elastomer (CASE) applications. In a traditional emulsion polymerization reaction, the surfactant does not become chemically bonded to the polymeric particles by carbon-carbon bond formation but rather remains in the polymeric particle product solution after the emulsion polymerization reaction is complete, i.e., all of the monomer(s) is reacted. The unreacted surfactant can have a detrimental effect on the polymer product solution, as it can interfere with the performance of such polymerization products in CASE applications; the suspension of polymeric particles may become destabilized over time and undergo unwanted coagulation. The unreacted surfactant may cause unwanted pealing of a latex paint coating on a substrate, and decreased moisture and scrubability resistance in other various CASE applications. Additionally, residual surfactant can cause an undesirable "blooming" that leads to surface irregularities in a resulting CASE material that is applied to a substrate.
Several proposals have been made in the prior art to employ a polymerizable surfactant as the surface active agent during an emulsion polymerization reaction. U.S. Pat. No. 5,478,883 (incorporated herein by reference in its entirety) describes the use of ethylenically unsaturated polymerizable water-soluble nonionic surfactants formed by the reaction of a diallylamine compound with ethylene oxide, propylene oxide or butylene oxide, in emulsion polymerization reactions. Similarly, U.S. Pat. No. 5,162,475 (incorporated herein by reference) provides alpha-beta ethylenically unsaturated poly(alkylenoxy) polymerizable surface active compounds for use in emulsion polymerization. For additional examples of polymerizable surfactants for use in emulsion polymerization processes, see U.S. Pat. Nos. 4,377,185 and 4,049,608.
Non-polymerizable surfactant solutions to the traditional problems encountered in performing an emulsion polymerization process are numerous. U.S. Pat. No. 3,941,857 describes the use of epoxy resins which react with the residual anionic, cationic or nonionic surfactant. Polymerizable compounds such as allyl alcohol (and esters thereof) have been found to be ineffective due to the formation of undesirable high levels of coagulum in the final emulsion polymerization product. Additionally, see U.S. Pat. No. 4,224,455.
Thus, there is a need for an emulsion polymerization process for forming polymers and discrete polymeric particles that are well suited for use in coatings (e.g., latex paints, electro-deposition, container, paper and paperboard, can coatings, industrial coatings, automotive coatings, textile coatings), adhesive (e.g., water- and non-water borne adhesives, pressure sensitive adhesives, binders), sealant (e.g. floor finishes, films, binders, non-woven binding materials such as carpet backing, glass fibers) and elastomer (CASE) applications.